#include <fstream>
using namespace std;
ifstream f("factorial.in");
ofstream g("factorial.out");
#include <cmath>
int sf(int n){
    int i = 1;
    int s = 0;
    while(floor(n/pow(5,i))){
        s += floor(n/pow(5,i));
        i++;
    }
    return s;
}

int main(){
    int p, n = 0;
    f >> p;
    while(sf(n) != p) n++;
    g << n;
    f.close();
    g.close();
    return 0;
}