#include<bits/stdc++.h>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
    int n, nr, mij, st, dr, ok=0, x, t;
    fin>>n;
    dr=n*6;
    st=0;
    if(n==0)fout<<1;
    else{
    while(st<=dr){
        mij=(dr+st)/2;
        x=0;
        nr=mij;
        while(nr){
            x+=nr/5;
            nr=nr/5;
        }
        if(x>=n){ok=1; t=mij; dr=mij-1;}
        else st=mij+1;
    }
        if(ok==0)fout<<-1;
        else fout<<t;
    }
}