#include <bits/stdc++.h>
int_fast64_t modu = (1e9) + 7;
int power(int x, unsigned int y) {
  int temp;
  if (y == 0) return 1;
  temp = power(x, y / 2);
  if (y % 2 == 0)
    return temp * temp;
  else
    return x * temp * temp;
}
void print_v(int x) { std::cout << x << " "; }
bool isluckyYear(int_fast64_t n) {
  int_fast64_t count = 0;
  while (n != 0) {
    if (n % 10 != 0) count++;
    n /= 10;
    if (count > 1) return false;
  }
  return true;
}
int_fast64_t countDigit(int_fast64_t n) { return floor(log10(n) + 1); }
int main() {
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(NULL);
  int_fast64_t n;
  std::cin >> n;
  if (n < 10)
    std::cout << 1;
  else {
    int_fast64_t countD = countDigit(n);
    int_fast64_t z = power(10, countD - 1);
    std::cout << (n % z == 0 ? z : z - n % z);
  }
  return 0;
}
