#include <fstream>
using namespace std;
ifstream fin ("fact.in");
ofstream fout ("fact.out");

long i, j, n, k, st, dr, m, s;


int main(){
    fin>>k;
    dr=0x7fffffff;
    st=1;
    while(st<=dr){
        m=(st+dr)/2;
        n=m;
        s=0;
        while(n){
            s=s+n/5;
            n=n/5;
        }
        if(s>=k){
            dr=m-1;
        }else{
            st=m+1;
        }
    }
    fout<<st;
}