#include <bits/stdc++.h>
using namespace std;

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

long long p;

int countingFive(int n){
    int s=0,five=5;
    while(n>=five){
        s+=n/five;
        five*=5;
    }
    return s;
}

int BS (int st, int dr, int p){
    int mij, poz=-1;
    while (st<=dr){
        mij = st + (dr-st) / 2;
        int Five=countingFive(mij);
        if (Five==p){
            poz=mij;
            dr=mij-1;
        }
        else
            if(Five>p)
                dr=mij-1;
            else
                st=mij+1;
    }
    return poz;
}

int main(){
    in>>p;
    out << BS(1,500000000,p);
    return 0;
}