#include <stdio.h>

const char *fin = "fact.in";
const char *fout = "fact.out";

unsigned int countZeros(unsigned int num) {
    unsigned int z = 0, pow = 5;
    while (pow <= num) {
        z += num / pow;
        pow *= 5;
    }
    return z;
}

int bins(unsigned int from, unsigned int to, unsigned int zeros) {
    if (from > to) {
        return -1;
    }
    int m = (from + to) / 2;
    unsigned int z = countZeros(m);
    if (z < zeros) {
        return bins(m + 1, to, zeros);
    } else if (z > zeros) {
        return bins(from, m - 1, zeros);
    } else {
        int p = bins(from, m - 1, zeros);
        if (p != -1) {
            return p;
        } else {
            return m;
        }
    }
}

int main() {
    unsigned int p = 0;
    FILE *f = fopen(fin, "rt");
    fscanf(f, "%d", &p);
    fclose(f);

    f = fopen(fout, "wt");
    //for (int i = 0; i <= p; ++i) {
        fprintf(f, "%d\n", bins(1, 5 * p + 1, p));
    //}
    fclose(f);
}