#include <iostream>
#include <fstream>

using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

long long P;

long long putere(int n){
    long long s=0,p=5;
    while(p <= n){
        s += n / p, p *= 5;
    }
    return s;
}

long long cb(long long p, long long u){
    long long m,poz=-1;
    int pt;
    while(p <=u){
        m=(p+u)/2;
        pt = putere(m);
        if(pt < P){
            p=m+1;
        }else{
            u=m-1;
            poz=m;
        }
    }
    return poz;
}


int main()
{
    bool stop = false;
    f >> P;
    long long i=1;
    if(P!=0)
    g << cb(0,P*5);
    else g << -1;

    return 0;
}