#include <stdio.h>

int main() {
  FILE *fin, *fout;
  int p, n, s, t;

  fin = fopen("fact.in", "r");
  fscanf(fin, "%d", &p);
  fclose(fin);

  n = 1;
  do {
    s = 0;
    t = 5;
    while(n / t > 0) {
      s += n / t;
      t *= 5;
    }
    n++;
  } while(s < p);

  fout = fopen("fact.out", "w");
  if(s == p)
    fprintf(fout, "%d\n", n - 1);
  else
    fprintf(fout, "1\n");
  fclose(fout);

  return 0;
}