
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

	public static void main(String[] args) {
		FastScanner sc = new FastScanner(System.in);

		String line = sc.nextLine();
		int count = 0;
		for (int i = 0; i < line.length(); i++) {
			if (line.charAt(i) == '1') {
				count++;
			}
		}
		System.out.println(count);
	}

	static class FastScanner {

		private BufferedReader reader = null;
	    private StringTokenizer tokenizer = null;

	    public FastScanner(InputStream in) {
	        reader = new BufferedReader(new InputStreamReader(in));
	        tokenizer = null;
	    }

	    public String next() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                tokenizer = new StringTokenizer(reader.readLine());
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }
	        return tokenizer.nextToken();
	    }

	    public String nextLine() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                return reader.readLine();
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }

	        return tokenizer.nextToken("\n");
	    }

	    public long nextLong() {
	        return Long.parseLong(next());
	    }

	    public int nextInt() {
	        return Integer.parseInt(next());
	    }

	    public double nextDouble() {
	         return Double.parseDouble(next());
	     }

	    public int[] nextIntArray(int n) {
	        int[] a = new int[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextInt();
	        return a;
	    }

	    public long[] nextLongArray(int n) {
	        long[] a = new long[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextLong();
	        return a;
	    }

	}


} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.StringTokenizer; StringTokenizer java.util public class Main {

	public static void main(String[] args) {
		FastScanner sc = new FastScanner(System.in);

		String line = sc.nextLine();
		int count = 0;
		for (int i = 0; i < line.length(); i++) {
			if (line.charAt(i) == '1') {
				count++;
			}
		}
		System.out.println(count);
	}

	static class FastScanner {

		private BufferedReader reader = null;
	    private StringTokenizer tokenizer = null;

	    public FastScanner(InputStream in) {
	        reader = new BufferedReader(new InputStreamReader(in));
	        tokenizer = null;
	    }

	    public String next() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                tokenizer = new StringTokenizer(reader.readLine());
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }
	        return tokenizer.nextToken();
	    }

	    public String nextLine() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                return reader.readLine();
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }

	        return tokenizer.nextToken("\n");
	    }

	    public long nextLong() {
	        return Long.parseLong(next());
	    }

	    public int nextInt() {
	        return Integer.parseInt(next());
	    }

	    public double nextDouble() {
	         return Double.parseDouble(next());
	     }

	    public int[] nextIntArray(int n) {
	        int[] a = new int[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextInt();
	        return a;
	    }

	    public long[] nextLongArray(int n) {
	        long[] a = new long[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextLong();
	        return a;
	    }

	}


} Main public static void main(String[] args) {
		FastScanner sc = new FastScanner(System.in);

		String line = sc.nextLine();
		int count = 0;
		for (int i = 0; i < line.length(); i++) {
			if (line.charAt(i) == '1') {
				count++;
			}
		}
		System.out.println(count);
	} main {
		FastScanner sc = new FastScanner(System.in);

		String line = sc.nextLine();
		int count = 0;
		for (int i = 0; i < line.length(); i++) {
			if (line.charAt(i) == '1') {
				count++;
			}
		}
		System.out.println(count);
	} FastScanner sc = new FastScanner(System.in); sc new FastScanner(System.in) String line = sc.nextLine(); line sc.nextLine() sc.nextLine sc int count = 0; count 0 for (int i = 0; i < line.length(); i++) {
			if (line.charAt(i) == '1') {
				count++;
			}
		} int i = 0; int i = 0; i 0 i < line.length() i line.length() line.length line i++ i++ i {
			if (line.charAt(i) == '1') {
				count++;
			}
		} {
			if (line.charAt(i) == '1') {
				count++;
			}
		} if (line.charAt(i) == '1') {
				count++;
			} line.charAt(i) == '1' line.charAt(i) line.charAt line i '1' {
				count++;
			} count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args static class FastScanner {

		private BufferedReader reader = null;
	    private StringTokenizer tokenizer = null;

	    public FastScanner(InputStream in) {
	        reader = new BufferedReader(new InputStreamReader(in));
	        tokenizer = null;
	    }

	    public String next() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                tokenizer = new StringTokenizer(reader.readLine());
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }
	        return tokenizer.nextToken();
	    }

	    public String nextLine() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                return reader.readLine();
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }

	        return tokenizer.nextToken("\n");
	    }

	    public long nextLong() {
	        return Long.parseLong(next());
	    }

	    public int nextInt() {
	        return Integer.parseInt(next());
	    }

	    public double nextDouble() {
	         return Double.parseDouble(next());
	     }

	    public int[] nextIntArray(int n) {
	        int[] a = new int[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextInt();
	        return a;
	    }

	    public long[] nextLongArray(int n) {
	        long[] a = new long[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextLong();
	        return a;
	    }

	} FastScanner private BufferedReader reader = null; reader null private StringTokenizer tokenizer = null; tokenizer null public FastScanner(InputStream in) {
	        reader = new BufferedReader(new InputStreamReader(in));
	        tokenizer = null;
	    } FastScanner {
	        reader = new BufferedReader(new InputStreamReader(in));
	        tokenizer = null;
	    } reader = new BufferedReader(new InputStreamReader(in)) reader new BufferedReader(new InputStreamReader(in)) tokenizer = null tokenizer null InputStream in in public String next() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                tokenizer = new StringTokenizer(reader.readLine());
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }
	        return tokenizer.nextToken();
	    } next {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                tokenizer = new StringTokenizer(reader.readLine());
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }
	        return tokenizer.nextToken();
	    } if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                tokenizer = new StringTokenizer(reader.readLine());
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
	            try {
	                tokenizer = new StringTokenizer(reader.readLine());
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        } try {
	                tokenizer = new StringTokenizer(reader.readLine());
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            } IOException e {
	                throw new RuntimeException(e);
	            } throw new RuntimeException(e); new RuntimeException(e) {
	                tokenizer = new StringTokenizer(reader.readLine());
	            } tokenizer = new StringTokenizer(reader.readLine()) tokenizer new StringTokenizer(reader.readLine()) return tokenizer.nextToken(); tokenizer.nextToken() tokenizer.nextToken tokenizer public String nextLine() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                return reader.readLine();
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }

	        return tokenizer.nextToken("\n");
	    } nextLine {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                return reader.readLine();
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }

	        return tokenizer.nextToken("\n");
	    } if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                return reader.readLine();
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        } tokenizer == null || !tokenizer.hasMoreTokens() tokenizer == null tokenizer null !tokenizer.hasMoreTokens() tokenizer.hasMoreTokens() tokenizer.hasMoreTokens tokenizer {
	            try {
	                return reader.readLine();
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        } try {
	                return reader.readLine();
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            } IOException e {
	                throw new RuntimeException(e);
	            } throw new RuntimeException(e); new RuntimeException(e) {
	                return reader.readLine();
	            } return reader.readLine(); reader.readLine() reader.readLine reader return tokenizer.nextToken("\n"); tokenizer.nextToken("\n") tokenizer.nextToken tokenizer "\n" public long nextLong() {
	        return Long.parseLong(next());
	    } nextLong {
	        return Long.parseLong(next());
	    } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next public int nextInt() {
	        return Integer.parseInt(next());
	    } nextInt {
	        return Integer.parseInt(next());
	    } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public double nextDouble() {
	         return Double.parseDouble(next());
	     } nextDouble {
	         return Double.parseDouble(next());
	     } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next public int[] nextIntArray(int n) {
	        int[] a = new int[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextInt();
	        return a;
	    } nextIntArray {
	        int[] a = new int[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextInt();
	        return a;
	    } int[] a = new int[n]; a new int[n] n for (int i = 0; i < n; i++)
	            a[i] = nextInt(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i a[i] = nextInt(); a[i] = nextInt() a[i] a i nextInt() nextInt return a; a int n n public long[] nextLongArray(int n) {
	        long[] a = new long[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextLong();
	        return a;
	    } nextLongArray {
	        long[] a = new long[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextLong();
	        return a;
	    } long[] a = new long[n]; a new long[n] n for (int i = 0; i < n; i++)
	            a[i] = nextLong(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i a[i] = nextLong(); a[i] = nextLong() a[i] a i nextLong() nextLong return a; a int n n public class Main {

	public static void main(String[] args) {
		FastScanner sc = new FastScanner(System.in);

		String line = sc.nextLine();
		int count = 0;
		for (int i = 0; i < line.length(); i++) {
			if (line.charAt(i) == '1') {
				count++;
			}
		}
		System.out.println(count);
	}

	static class FastScanner {

		private BufferedReader reader = null;
	    private StringTokenizer tokenizer = null;

	    public FastScanner(InputStream in) {
	        reader = new BufferedReader(new InputStreamReader(in));
	        tokenizer = null;
	    }

	    public String next() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                tokenizer = new StringTokenizer(reader.readLine());
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }
	        return tokenizer.nextToken();
	    }

	    public String nextLine() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                return reader.readLine();
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }

	        return tokenizer.nextToken("\n");
	    }

	    public long nextLong() {
	        return Long.parseLong(next());
	    }

	    public int nextInt() {
	        return Integer.parseInt(next());
	    }

	    public double nextDouble() {
	         return Double.parseDouble(next());
	     }

	    public int[] nextIntArray(int n) {
	        int[] a = new int[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextInt();
	        return a;
	    }

	    public long[] nextLongArray(int n) {
	        long[] a = new long[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextLong();
	        return a;
	    }

	}


} public class Main {

	public static void main(String[] args) {
		FastScanner sc = new FastScanner(System.in);

		String line = sc.nextLine();
		int count = 0;
		for (int i = 0; i < line.length(); i++) {
			if (line.charAt(i) == '1') {
				count++;
			}
		}
		System.out.println(count);
	}

	static class FastScanner {

		private BufferedReader reader = null;
	    private StringTokenizer tokenizer = null;

	    public FastScanner(InputStream in) {
	        reader = new BufferedReader(new InputStreamReader(in));
	        tokenizer = null;
	    }

	    public String next() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                tokenizer = new StringTokenizer(reader.readLine());
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }
	        return tokenizer.nextToken();
	    }

	    public String nextLine() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                return reader.readLine();
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }

	        return tokenizer.nextToken("\n");
	    }

	    public long nextLong() {
	        return Long.parseLong(next());
	    }

	    public int nextInt() {
	        return Integer.parseInt(next());
	    }

	    public double nextDouble() {
	         return Double.parseDouble(next());
	     }

	    public int[] nextIntArray(int n) {
	        int[] a = new int[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextInt();
	        return a;
	    }

	    public long[] nextLongArray(int n) {
	        long[] a = new long[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextLong();
	        return a;
	    }

	}


} Main

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

	public static void main(String[] args) {
		FastScanner sc = new FastScanner(System.in);

		String line = sc.nextLine();
		int count = 0;
		for (int i = 0; i < line.length(); i++) {
			if (line.charAt(i) == '1') {
				count++;
			}
		}
		System.out.println(count);
	}

	static class FastScanner {

		private BufferedReader reader = null;
	    private StringTokenizer tokenizer = null;

	    public FastScanner(InputStream in) {
	        reader = new BufferedReader(new InputStreamReader(in));
	        tokenizer = null;
	    }

	    public String next() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                tokenizer = new StringTokenizer(reader.readLine());
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }
	        return tokenizer.nextToken();
	    }

	    public String nextLine() {
	        if (tokenizer == null || !tokenizer.hasMoreTokens()) {
	            try {
	                return reader.readLine();
	            } catch (IOException e) {
	                throw new RuntimeException(e);
	            }
	        }

	        return tokenizer.nextToken("\n");
	    }

	    public long nextLong() {
	        return Long.parseLong(next());
	    }

	    public int nextInt() {
	        return Integer.parseInt(next());
	    }

	    public double nextDouble() {
	         return Double.parseDouble(next());
	     }

	    public int[] nextIntArray(int n) {
	        int[] a = new int[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextInt();
	        return a;
	    }

	    public long[] nextLongArray(int n) {
	        long[] a = new long[n];
	        for (int i = 0; i < n; i++)
	            a[i] = nextLong();
	        return a;
	    }

	}


}
