#include<stdio.h>
#include<ctype.h>
int main(void)
{
    FILE *f;
    f = fopen("fact.in", "rb");
    int  fact = 1, nr = 0, p, i = 2, u, rez;
    printf("p = ");
    scanf("%d", &p);
    if ( p == 0)printf("n = 1");
    else
    {
        while(nr < p )
        {
            fact  = fact * i;
            i ++;
            u = fact % 10;
            while(u == 0)
            {
                nr ++;
                fact =  fact / 10;
                u = fact % 10;
            }
        }
        rez = i -1;
        printf("n = %d", rez);
    }
    fclose(f);
    return 0;

}