#include <fstream>

using namespace std;

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

long long n, p, mij;



int main()
{
    in>>p;
    long long st=1, dr=1000000000;
    while(st<=dr){
        mij=(st+dr)/2;
        int q=5, s=0;
        while(q<=mij){
            s+=mij/q;
            q*=5;
        }
        if(s<p)
            st=mij+1;
        else dr=mij-1;
    }
    out<<st;
}