#include <cstdio>
using namespace std;

int p;

int cauta_b(int l,int r)
{
    int k=(l+r)/2,n=k,ok=0;
        while(n/5!=0)
        {
            n/=5;
            ok+=n;
        }
        if(ok==p)
        return k;
        else if(ok>p) cauta_b(l,k);
        else cauta_b(k+1,r);
}

int main()
{
    int i,n,ok;
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%d",&p);
    if(p==0)
    {
        printf("1");
        return 0;
    }
    n=cauta_b(p,100000000);
    printf("%d",n);
    fclose(stdout);
    return 0;
}