#include <stdio.h>

int main(){
  FILE *i, *o;
  i = fopen("fact.in", "r");
  o = fopen("fact.out", "w");
  long long r = -1, s= 1 , f= 1000000000, p, m, zr, q;
  fscanf(i, "%ll", &p);
  while ( s<=f ){
    m = (s+f)/2;
    zr = 0;
    for (q = 5; q<=m; q*=5) zr += (m/q);
    if (zr == p) {r = m; f=m-1;}
    else if (zr > p) f = m-1;
    else s = m+1;
  }
  fprintf(o, "%ll", r);

  return 0;
}