#include <bits/stdc++.h>

using namespace std;
ifstream in  ("fact.in");
ofstream out("fact.out");

int verif(int x){
    int nr=0;
    while(x>0){
        nr+=x/5;
        x/=5;
    }
    return nr;
}

int main(){
    int p;
    in>>p;
    if(p==0){
        out<<1;
        return 0;
    }

    int st=1,dr=5*p,rez=-1;
    while(st<=dr){
        int mij=(st+dr)/2;
        if(verif(mij)<p){
            st=mij+1;
        }
        else{
            rez=mij;
            dr=mij-1;
        }
    }
    out<<rez;
}