#include <iostream>
#include <cmath>
#include <fstream>

std::ifstream fin("fact.in");
std::ofstream fout("fact.out");

unsigned long long Binary_Exp(unsigned long long a, unsigned long long b) {
    unsigned long long thing = 1;
    while (b>0){
        if (b&1) {thing*=a;}
        a*=a;
        b >>=1;
    }
    return thing;
}

unsigned long long Zero_La_Final_Fact(unsigned int n) {
    if (n<5) {
        return 0;
    }
    unsigned long long s=0,p=1;
    while (Binary_Exp(5,p)<=n){
        s+=std::floor(n/Binary_Exp(5,p));
        p++;
    }
    return s;
}

int main()
{
    unsigned int p;
    fin >> p;
    if (p>24999999) {
        fout << -1;
    } else {
        unsigned int r=24999999,l=1,probe=(l+r)/2;
        while (l<r) {
            if (Zero_La_Final_Fact(probe)==p) {
                fout << probe;
                break;
            } else if( Zero_La_Final_Fact(probe)<p) {
                l=probe+1;
            } else if ( Zero_La_Final_Fact(probe)>p) {
                r=probe-1;
            }
        }
    }
    return 0;
}