C++ :

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