#include <stdio.h>

int fact (int n)
{
    int i, a, b, c=0;
    for (i=1; i<=n; i++) {
        a=i;
        b=0;
        while (a%5==0) {
            b++;
            a/=5;
        }
        c+=b;
    }
    return c;
}

int main ()
{
    freopen("fact.in", "r", stdin);
    freopen("fact.out", "w", stdout);
    int p, st, dr, t;
    scanf("%d", &p);
    st=1;
    dr=100;
    while (st<=dr) {
        t=st+dr/2;
        if (p==fact(t)) {
            while (p==fact(t)) {
                t--;
            }
            printf ("%d", t+1);
            break;
        } else if (p<fact(t)) {
            dr=t-1;
        } else {
            st=t+1;
        }
    }
    return 0;
}