#include <cstdio>

int P, N, step;

int trailingZeroes(int N)
{
    for(int i = 5, z = 0;; i *= 5)
    {
        z += N / i;

        if(i > N) return z;
    }
};

int main(){

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

    scanf("%d", &P);

    for(step = 1; step < 400000015; step <<= 1);

    for(N = 400000015; step; step >>= 1)

        if(trailingZeroes(N - step) >= P) N -= step;

    printf("%d", P ? N : 0);

    return 0;
}