#include <bits/stdc++.h>
using namespace std;
const double pi = 2 * acos(0.0);
double inff = 1.0 / 0.0;
long long int x, y, m, n, i, j, k, t, w, u, c;
long long int a[1000001];
long long int num(long long int x) {
  while (x > 0) {
    x /= 10;
    c++;
  }
  return c;
}
int main(void) {
  cin >> n;
  t = num(n);
  if (t == 1) {
    cout << 1 << "\n";
    return 0;
  }
  y = (long long int)pow(10, t - 1);
  n %= y;
  cout << (y - n) << "\n";
}
