#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int cinci(int n)
{
    int cont = 0;
    while(n % 5 == 0)
    {
        n /= 5;
        cont ++;
    }

    return cont;
}
int main()
{
    int fact=0, zero = 0;
    int p;
    FILE *f = fopen("fact.in", "r");
    FILE *g = fopen("fact.out", "w");

    fscanf(f, "%d", &p);

    while( p > zero)
    {
        fact += 5;
        zero += cinci(fact);
    }

    fprintf(g, "%d", fact);

    return 0;
}