#include <fstream>

using namespace std;

int cinci(int n){
    int r=0;
    while(n%5==0){
        n/=5;
        r++;
    }
    return r;
}

int main()
{
    ifstream in("fact.in");
    ofstream out("fact.out");
    long long n,k=0,nr=0;
    in>>n;
    if(n==0)out<<1;
    else {
    while (nr<n){
        k++;
        nr+=cinci(k);
    }

    out<<k;
    }
    in.close();
    out.close();
    return 0;
}