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

long long zero(long long x)
{
    long long s=0;
    for (long long i=5; i<=x; i*=5)
        s=s+(x/i);
    return s;
}
int main()
{
    long long p,x,y,mij;
    in>>p;
    x=1;
    y=5*p;
    while (x<=y){
        m=(x+y)/2;
        if(zero(m)<p){
            x=m+1;
        }
        else {
            y=m-1;
        }
    }
    if (zero(x)==p){
        out<<y;
    }
    else {
        out<<-1;
    }
    return 0;
}