#include<stdio.h>
int main()
{
    int n = 2, fact = 1, nr = 0, p, i, u, k;
    printf("p = ");
    scanf("%d", &p);

    for( i = 1; i < n; i ++)
    {
        fact = fact * i;
        if(fact / 5 == 0)
        {
            u = fact % 10;
            while(u == 0)
            {
                nr ++;
                fact = fact / 10;
                u = fact % 10;
            }
            if(nr == p)
                break;
        }
        n ++;
    }
    k = n-1;
    if(p == 0)printf("fact = 1");
    else printf("%d ", k );
    return 0;

}