C++ :

#include <cstdio>
typedef long long ll;
static ll a[1000005];
int main(){
    int N; ll M;
    if(scanf("%d %lld", &N, &M) != 2) return 0;
    ll hi = 0;
    for(int i=0;i<N;i++){ scanf("%lld", &a[i]); if(a[i] > hi) hi = a[i]; }
    ll lo = 0, ans = 0;
    while(lo <= hi){
        ll mid = lo + (hi - lo) / 2;
        ll got = 0;
        for(int i=0;i<N;i++) if(a[i] > mid) got += a[i] - mid;
        if(got >= M){ ans = mid; lo = mid + 1; }
        else hi = mid - 1;
    }
    printf("%lld\n", ans);
    return 0;
}