#include <bits/stdc++.h>

using namespace std;
const long long NMAX = 400000015;
long long nr(long long p)
{
    long long j,sum=0;
    for (j = 5; p/j>=1; j*=5)
        sum+=p/j;
    return sum;
}
ifstream in("fact.in");
ofstream out("fact.out");

int main()
{
    long long p,st,dr,mj,poz = -1;
    in >> p;
    st = 1;
    dr = NMAX;
    while (st<=dr)
    {
        mj = (st+dr)/2;
        long long val = nr(mj);
        if (val>p)
            dr = mj-1;
        else if (val<p)
            st = mj+1;
        else
        {
            poz = mj;
            dr = mj-1;
        }
    }
    out << poz;
}