#include <fstream>
#include <iostream>

using namespace std;

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

    int p, a=5,ca, nrDe5=0;
    fin>>p;
    while(nrDe5<=p){
            ca=a;
        while(ca%5==0){
            ca=ca/5;
            nrDe5++;
            if(nrDe5==p) break;
        }
        if(nrDe5==p) break;
        a++;

    }
    fout<<a;
    fin.close();
    fout.close();
    return 0;


}