#include <stdio.h>
#include <assert.h>

long long average (long long a, long long b, long long c)
{
    long long n=0;
    n= a / 3 + b / 3 + c / 3 + (a % 3 + b % 3 + c % 3) / 3;
    return n;
}

int main(void)
{
    long long a=9223372036854775800;
    long long b=4611686018427387897;
    long long c=3;
    
    printf("%lld\n", average(a, b, c));
    printf("%lld\n", 4611686018427387900);
    
    assert (average ( 9223372036854775800, 4611686018427387897, 3 ) == 4611686018427387900 );
}