#include <iostream>
#include <fstream>

using namespace std;

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

int n,P;

int zero(int x){
    int Nrz=0,put=1;
    while (put<=x){
        put*=5;
        Nrz+=(x/put);
    }
    return Nrz;
}

int caut(int st, int dr){
    int a=-1,zr;
    while (st<=dr){
        int mij=(st+dr)/2;
        zr=zero(mij);
        if (zr==P){
            a=mij;
            dr=mij-1;
        }
        else if (zr>P) dr=mij-1;
        else if (zr<P) st=mij+1;
    }
    return a;
}

int main()
{
    in>>P;
    out<<caut(1, 100000000);
    return 0;
}