#include <cstdio>

using namespace std;

int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    int p,a=1,i=1,cont=0;
    scanf("%d",&p);
    while(i)
    {
        a=a*i;
        if(a%10==0)
        {
            ++cont;
            a/=10;
        }
        if(cont==p)
        {
            break;
        }
        else
            ++i;
    }
    printf("%d",i);
    return 0;
}