#include <stdio.h>

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

int hasZeros(unsigned int num, unsigned int zeros) {
    unsigned int z = 0, pow = 5;
    while (pow <= num) {
        z += num / pow;
        pow *= 5;
    }
    return (z >= zeros) ? 1 : 0;
}

int bins(unsigned int from, unsigned int to, unsigned int zeros) {
    if (from >= to) {
        return from;
    }
    int m = (from + to) / 2;
    if (hasZeros(m, zeros)) {
        return bins(from, m, zeros);
    }
    return bins(m + 1, to, zeros);
}

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

    f = fopen(fout, "wt");
    fprintf(f, "%d", bins(1, 5 * p + 1, p));
    fclose(f);
}