#include <stdio.h>
#include <stdlib.h>
int factorial(int a)
{
    int c=a;
    for(int i=1; i<a; i++)
        c=c*i;


    return c;

}
int numar_zerouri(int b)
{
    int nr=0;
    while(b%10==0)
    {
        nr++;
        b=b/10;
    }
    return nr;

}
int main()
{
    FILE *f;
    f=fopen("fact.in.txt","r");
    double p;
    int x=0;
    if(fscanf(f,"%lf",&p)!=EOF)
    {
        x++;
    };
    int ok=0;
    fclose(f);
    FILE *q;
    q=fopen("fact.out.txt","w");
    while(ok==0)
    {
        int m;
        m=factorial(x);


        if(numar_zerouri(m)==p)
        {
            ok=1;
            fprintf(q,"%d",x);
        }
        else
            x++;
    }
    fclose(q);
    return 0;
}