#include <cstdio>

int f(int n){

  int i, aux = 0;
  for(i = 5; i <= n; i *= 5)
    aux += n/i;

  return aux;
}

int bin(int left, int right, int key){

  int mid;
  
  while(left < right){
    mid = left+((right-left)>>1);
    if(f(mid) <= key)
      left  = mid+1;
    else
      right = mid-1;
  }
  mid = left+((right-left)>>1);

  if(f(mid) > key)
    mid--;
  if(f(mid) == key)
    return mid;
  return -1;

}

int main(){

  freopen("fact.in", "r", stdin);
  freopen("fact.out", "w", stdout);

  int N;

  scanf("%d", &N);
  printf("%d\n", bin(1, 1000, N));

  return 0;

}