#include <fstream>
using namespace std;
ifstream in("fact.in");
ofstream o("fact.out");


int p;
int calc(int n){
    int ct=0;
    while(n){
        ct+=n/5;
        n/=5;
    }
    return ct;
}
int main()
{
    in >> p;
    int st = 0,dr = 100000000000;
    while(st<=dr){
        int m=(st+dr)/2;
        if(calc(m)<p)
            st = m+1;
        else
            dr = m-1;
    }

    o << st?1:(calc(st)==p)?st:-1;
    return 0;
}