#include <fstream>
using namespace std;

int zero(int k){
    long m = 5, z = 0;
    while(k/m != 0){
        z+=k/m;
        m *= 5;
    }
    return z;
}

int main()
{
    int P, nrz = 1, N = 1;
    ifstream f("fact.in");
    ofstream g("fact.out");
    f>>P;
    while(nrz != P){
        nrz = zero(N);
        N++;
        if(nrz == P){
            N--;
        }
    }
    g<<N;
}