#include <bits/stdc++.h>
using namespace std;
long long mod(long long a, long long b) {
  if (a % b < 0) {
    return a % b + b;
  }
  return a % b;
}
long long mod_exp(long long a, long long b, long long c) {
  long long res = 1;
  a = a % c;
  while (b > 0) {
    if (b % 2 == 1) {
      res = (res * a) % c;
    }
    b /= 2;
    a = (a * a) % c;
  }
  return res;
}
long long mymod(long long a, long long b) { return ((a % b) + b) % b; }
bool prime[200001];
void SieveOfEratosthenes() {
  prime[1] = false;
  for (int p = 2; p * p <= 200000; p++) {
    if (prime[p] == true) {
      for (int i = p * p; i <= 200000; i += p) prime[i] = false;
    }
  }
  return;
}
long long powe[200005];
void power() {
  powe[0] = 1;
  for (long long i = 1; i < 200005; i++) {
    powe[i] = mymod(2 * powe[i - 1], 1000000007);
  }
}
long long gcdExtended(long long, long long, long long *, long long *);
long long modInverse(long long a, long long m) {
  long long x, y;
  long long g = gcdExtended(a, m, &x, &y);
  long long res = (x % m + m) % m;
  return res;
}
long long gcdExtended(long long a, long long b, long long *x, long long *y) {
  if (a == 0) {
    *x = 0, *y = 1;
    return b;
  }
  long long x1, y1;
  long long gcd = gcdExtended(b % a, a, &x1, &y1);
  *x = y1 - (b / a) * x1;
  *y = x1;
  return gcd;
}
map<pair<long long, long long>, long long> edgeweight;
struct node {
  vector<long long> adj;
  long long dist;
  long long parent;
  long long outtime;
};
struct edges {
  long long src;
  long long to;
  long long weight;
};
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long k, b, n, t;
  cin >> k >> b >> n >> t;
  long long ans = n;
  long long st = 1;
  long long en = k * st + b - 1;
  while (true) {
    if (st <= t && t <= en) {
      cout << ((0 > ans) ? 0 : ans) << "\n";
      exit(0);
    }
    ans--;
    st = en + 1;
    en = k * st + b - 1;
  }
  return 0;
}
