#include <bits/stdc++.h>
using namespace std;
vector<bool> prime;
vector<long long> fact, inv, primes, factors, pf;
void fast() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
}
void factorize(long long a) {
  factors.clear();
  for (long long i = 1; i * i <= a; i++) {
    if (i * i == a)
      factors.push_back(i);
    else if (a % i == 0) {
      factors.push_back(i);
      factors.push_back(a / i);
    }
  }
  sort(factors.begin(), factors.end());
}
long long power(long long a, long long b) {
  if (a == 1 || b == 0) return 1;
  long long c = power(a, b / 2);
  long long res = 1;
  res = c * c;
  if (res >= 1000000007) res %= 1000000007;
  if (b % 2) res *= a;
  if (res >= 1000000007) res %= 1000000007;
  return res;
}
long long modInv(int a) { return power(a, 1000000007 - 2); }
void factorial(long long n) {
  fact.resize(n + 1);
  fact[0] = 1;
  for (long long i = 1; i <= n; i++) {
    fact[i] = fact[i - 1] * i;
    if (fact[i] >= 1000000007) fact[i] %= 1000000007;
  }
}
void InvFactorial(long long n) {
  inv.resize(n + 1);
  inv[0] = 1;
  for (long long i = 1; i <= n; i++) inv[i] = modInv(fact[i]);
}
long long ncr(long long n, long long r) {
  if (n < r || n < 0 || r < 0) return 0;
  long long b = inv[n - r];
  long long c = inv[r];
  long long a = fact[n] * b;
  if (a >= 1000000007) a %= 1000000007;
  a *= c;
  if (a >= 1000000007) a %= 1000000007;
  return a;
}
void remove_duplicates(vector<pair<long long, long long> > &v) {
  sort(v.begin(), v.end());
  long long _size = unique(v.begin(), v.end()) - v.begin();
  v.resize(_size);
}
unsigned long long gcd(unsigned long long u, unsigned long long v) {
  if (u == 0 || v == 0) return max(u, v);
  unsigned long long shift = __builtin_ctz(u | v);
  u >>= __builtin_ctz(u);
  do {
    v >>= __builtin_ctz(v);
    if (u > v) swap(u, v);
    v -= u;
  } while (v != 0);
  return u << shift;
}
void sieve(long long n) {
  prime.assign(n + 1, 1);
  prime[1] = false;
  for (long long p = 2; p * p <= n; p++) {
    if (prime[p]) {
      for (long long i = p * p; i <= n; i += p) prime[i] = false;
    }
  }
  for (long long i = 2; i < n + 1; i++) {
    if (prime[i]) primes.push_back(i);
  }
}
void prime_sieve(long long n) {
  pf.assign(n + 1, 0);
  for (long long i = 0; i < n + 1; i++) pf[i] = i;
  for (long long i = 2; i <= n; i++) {
    if (pf[i] == i) {
      for (long long j = i; j <= n; j += i) pf[j] = i;
    }
  }
}
long long size(long long l) {
  long long p = l;
  long long count = 0;
  while (p) p /= 10, count++;
  return count;
}
void solve() {
  long long k, b, n, t;
  cin >> k >> b >> n >> t;
  long long mul = 1;
  if (k == 1) {
    cout << max(0ll, (n * b + b - t) / b);
    return;
  }
  cout << max(
      0ll, n - (long long)floor(log((t * (k - 1) + b) / (k + b - 1)) / log(k)));
}
int main() {
  long long T = 1;
  for (long long z = 1; z <= T; z++) solve();
}
