import java.io.*;
import java.util.*;
import javax.swing.text.InternationalFormatter;
import java.math.*;

public class test {

    public static PrintWriter out;
    static class pair implements Comparable<pair> {
    int i = 0;
    int v = 0;
    pair(int b, int a) {
    this.i = b;
    this.v = a;
    }
    @Override
    public int compareTo(pair o) {
        return o.v-this.v;
    }
    }

    public static void main(String[] args) throws IOException
    {
        Reader scn = new Reader();
       int n = 5;
       int[] arr = scn.nextIntArray(n);
       int r = arr[0];
       double d = Math.sqrt((arr[1]-arr[3])*(arr[1]-arr[3])+(arr[2]-arr[4])*(arr[2]-arr[4]));
       double ans  = Math.ceil(d/(2*r));
       System.out.println((int)ans);

    }

    





// _________________________TEMPLATE_____________________________________________________________
public static class Reader {
final private int BUFFER_SIZE = 1 << 16;
private DataInputStream din;
private byte[] buffer;
private int bufferPointer, bytesRead;

public Reader() {
din = new DataInputStream(System.in);
buffer = new byte[BUFFER_SIZE];
bufferPointer = bytesRead = 0;
}

public Reader(String file_name) throws IOException {
din = new DataInputStream(new FileInputStream(file_name));
buffer = new byte[BUFFER_SIZE];
bufferPointer = bytesRead = 0;
}

public String readLine() throws IOException {
byte[] buf = new byte[100000 + 1]; // line length
int cnt = 0, c;
while ((c = read()) != -1) {
if (c == '\n')
break;
buf[cnt++] = (byte) c;
}
return new String(buf, 0, cnt);
}

public int nextInt() throws IOException {
int ret = 0;
byte c = read();
while (c <= ' ')
c = read();
boolean neg = (c == '-');
if (neg)
c = read();
do {
ret = ret * 10 + c - '0';
} while ((c = read()) >= '0' && c <= '9');

if (neg)
return -ret;
return ret;
}

public long nextLong() throws IOException {
long ret = 0;
byte c = read();
while (c <= ' ')
c = read();
boolean neg = (c == '-');
if (neg)
c = read();
do {
ret = ret * 10 + c - '0';
} while ((c = read()) >= '0' && c <= '9');
if (neg)
return -ret;
return ret;
}

public double nextDouble() throws IOException {
double ret = 0, div = 1;
byte c = read();
while (c <= ' ')
c = read();
boolean neg = (c == '-');
if (neg)
c = read();

do {
ret = ret * 10 + c - '0';
} while ((c = read()) >= '0' && c <= '9');

if (c == '.') {
while ((c = read()) >= '0' && c <= '9') {
ret += (c - '0') / (div *= 10);
}
}

if (neg)
return -ret;
return ret;
}

private void fillBuffer() throws IOException {
bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
if (bytesRead == -1)
buffer[0] = -1;
}

private byte read() throws IOException {
if (bufferPointer == bytesRead)
fillBuffer();
return buffer[bufferPointer++];
}

public void close() throws IOException {
if (din == null)
return;
din.close();
}

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

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

public int[][] nextInt2DArray(int m, int n) throws IOException {
int[][] arr = new int[m][n];
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++)
arr[i][j] = nextInt();
}
return arr;
}

public void printarr(int[] arr) {
            StringBuilder t = new StringBuilder();
            StringBuilder ans = new StringBuilder();
            for (int i = 0; i < 50; i++)
                t.append('-');
            System.out.print(t);
            System.out.println();
            for (int i = 0; i < arr.length - 1; i++) {

                ans.append(arr[i]);
                ans.append('-');

            }
            System.out.print(ans);
            System.out.print(arr[arr.length - 1]);
            System.out.println();
            System.out.print(t);
        }
}

}