#include <fstream>

using namespace std;

fstream in ("fact.in" , ios::in ),
        out("fact.out", ios::out);

long long p;

long long zero(long long x);

int main(){

    in >> p;

    long long pas = 1LL<<32LL, i=0;

    while( pas ){

        if( zero( pas+i ) < p ){

            i+=pas;
        }

        pas/=2LL;
    }

    if( zero( i+1LL ) == p )
        out << i+1LL <<'\n';
    else
        out << "-1";

    return 0;
}


long long zero(long long x){

    long long rez = 0;

    while( x>=5LL ){

        rez += x/5LL;
        x /= 5LL;
    }

    return rez;
}