#include <iostream>
#include <fstream>
#include <math.h>
#define X 10000
using namespace std;

int main(){
    int n,p,k=1,l,pp,o=0;
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    fin>>p;
    for (n=1; o<p; ++n){
        k*=n;
        if (k%10==0){
            ++o;
            k/=10;
        }
    }
    if (p<=0)
        cout<<"-1";
    else fout<<n-1;
}