#include <cstdio>
#include <cstring>
using namespace std;

int nr0(long long int n)
{
    int i=0;
    while(n%10==0)
    {
        i++;
        n=n/10;
    }
    return i;
}

int main()
{
    FILE *fin = fopen("fact.in", "r");
    FILE *fout = fopen("fact.out", "w");
    int p,n=1,ok=0,i;
    long long int fac=1;
    fscanf(fin, "%d", &p);
    while(ok==0)
    {
        for(i=1;i<=n;i++)
        fac=fac*i;
        if(nr0(fac)==p)
        ok=1;
        else
        n++;
        fac=1;
    }
    fprintf(fout, "%d", n);
    fclose(fin);
    fclose(fout);
    return 0;
}