#include <bits/stdc++.h>

using namespace std;

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

unsigned long long p,m,li,ls,k,i,FINAL;

int main()
{
    fin >> p;
    li=1;
    ls=5*p+5;
    while(li<=ls)
    {
        m=(li+ls)/2;
        k=0;
        for(i=5;i<=m;i*=5)
            k+=m/i;
        if(k==p)
            FINAL = m;
        if(k<p)
            li=m+1;
        else ls=m-1;
    }
    if(FINAL==0)
        fout << "-1";
    else
        fout << FINAL;
    return 0;
}