#include <cstdio>
#include <cmath>
using namespace std;

inline int zerosAtEndOfFact (int x) {
    int i = 1, s = 0;
    while (true) {
        float r = x / pow(5, i);
        if (r < 1) {
            break;
        }
        s += floor(r);
        if (i == 1) {
            i++;
        } else {
            i += 2;
        }
    }
    return s;
}

int main () {
    int P, i = 1;

    freopen("fact.in", "r", stdin);
    freopen("fact.out", "w", stdout);

    scanf("%d", &P);

    while (true) {
        if (zerosAtEndOfFact(i) == P) {
            printf("%d", i);
            break;
        }
        i++;
    }

    return 0;
}