#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp> // Common file 
#include <ext/pb_ds/tree_policy.hpp> 
#include <functional> // for less
using namespace std;
using namespace __gnu_pbds;
#define IOS ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define endl "\n"
#define int long long 
// int dx[]={-1,1,0,0}; int dy[]={0,0,1,-1};
// int dx[]={2,2,-2,-2,1,1,-1,-1}; int dy[]={1,-1,1,-1,2,-2,2,-2};
const long long mod = 1e9 + 7;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef pair<int, int> ii;
typedef vector< pair< int, int > > vii;
typedef map<int, int> mii;
typedef pair<int, ii> pip;
typedef pair<ii, int> ppi;
#define arrinp(arr,init,final,size,type) type* arr=new type[size];for(int i=init;i<final;i++)cin>>arr[i];
#define cr2d(arr,n,m,t) t**arr=new t*[n];for(int i=0;i<n;i++)arr[i]=new t[m];
#define w(t) int t;cin>>t; while(t--)
#define takeInp(n) int n;cin>>n;
#define fr(i,init,final) for(int i=init;i<final;i++)
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define all(c) (c).begin(),(c).end()
#define rall(c) (c).rbegin(),(c).rend()
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>  nds; 
vi init(string s)
{
	istringstream sin(s);
	int n;
	vi arr;
	while(sin>>n)arr.push_back(n);
	return arr;
}
int pow(int x, int y)
{ 
	if(y==0)return 1;
	int u=pow(x,y/2);
	u=u*u;
	if(y%2)u=x*u;
	return u;
    
}
int gcd(int a,int b)
{
	if(a<b)return gcd(b,a);
	return (b==0?a:(a%b?gcd(b,a%b):b));
}
int gcd_e(int a,int b,int &x,int &y)
{
	
	if(b==0){x=1; y=0; return a;}
	int x1,y1;
	int p=gcd_e(b,a%b,x1,y1);
	x=y1;
	y=x1-(a/b)*y1;
	return p;
}
	int k,b,n,t;
int val(int xx)
{   int p=pow(k,xx);
	return p*t+b*(xx==1?xx:(p-1)/(k-1));
	
}
signed main()
{
		
long 	double  k,b,n,t;
cin>>k>>b>>n>>t;
if(k!=1)
cout<<(ceil(n-log((t*(k-1)+b)/(k-1+b))/log(k)))<<endl;
else cout<<ceil((1+b*n-t)/b)<<endl;
	
}

