#include <iostream>
#include <cstdio>
using namespace std;
long long p;
int Nrz(int x){
    int p,d;
    d = 0; p = 5;
    while (x/p)
        {
            d+=(x/p);
            p*=5;
        }
    return d;
}
int main(){
    int st,dr,m,i;
    freopen("factorial.in","r",stdin);
    freopen("factorial.out","w",stdout);
    scanf("%lld",&p);
    st = 1; dr = 100; i = -1;
    while(st <= dr)
    {
        m = (st+dr)/2;
        if(Nrz(m) < p)
         st = m+1;
        else if(Nrz(m) > p)
         dr = m-1;
        else if(Nrz(m) == p)
         {i = m;dr=m-1;}
    }
    printf("%d\n",i);
    return 0;
}