#include <iostream>
#include <fstream>
using namespace std;
ifstream hin("fact.in");
ofstream hout("fact.out");
int f(int n)
{
    int p5=5, rez=0;
    while(n/p5>0)
    {
        rez=rez+n/p5;
        p5=p5*5;
    }
    return rez;
}
int main()
{
    int n, p, i,st, dr, mij, a;
    hin>>p;
    st=1; dr=5*p;
    while( st<= dr)
    {
        mij=(st+ dr)/2;
        if(f(mij)<p)
            st=mij+1;
        else
            dr=mij-1;

    }
    if( f(st)==p)
        hout<< st;
    else
        hout<< -1;
    return 0;
}