#include <fstream>
using namespace std;
int p,e,i,sol;
int main (){
    ifstream fin ("fact.in");
    ofstream fout ("fact.out");
    fin>>p;
    if (p==0){
        fout<<1;
        return 0;
    }
    i=1;
    while (sol!=p){
        e=i;
        while (e%5==0){
            sol++;
            e/=5;
        }
        i++;
    }
    fout<<i-1;
}