#include <iostream>
#include <math.h>

using namespace std;

int main(){

    int n = 1, t, i;
    float p;


    FILE *f = fopen ("fact.in", "r");
    FILE *g = fopen ("fact.out", "w");

    fscanf (f, "%f", &p);
    i = 0;
    t =trunc (pow (10, p)) ;

    do {
        ++i;
        n *= i;
        }
    while (n % t != 0);

    fprintf (g, "%d", i);


    return 0;
}