#include <fstream>

using namespace std;

int zerofactorial(int x)
{
    int k5, nr;
    k5 = 0;
    for (int i = 1; i <= x; i++){
        nr = i;
        if (nr % 5 == 0){
            k5 = k5 + 1;
            nr = nr / 5;
            
        }
    }
    return k5+1;
}

/*int putere (int a, int b)
{
    int nr;
    for ( int j = 1; j <= b; j++){
        nr = nr * b;
    }
    return nr;
} */

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