#include <stdio.h>

int main()
{
    int N;
    scanf("%d", &N);
    
    int minB = 5000;
    for (int i=0; i<=(N/3); i++)
    {
        int kg = i*3;
        int kgRe = N - (kg);
        if (kgRe%5==0)
        {
            int B = i+kgRe/5;
            if (B<minB)
            {
                minB = B;
            }
        }
    }
    if (minB==5000)
        printf("-1");
    else
        printf("%d", minB);
    return 0;
}