Aggressive cows

#include<stdio.h>
#include<stdlib.h>
int N, C;
long long int loca[100000];

int compare(const void* a, const void* b) {
    return *(long long int*)a - *(long long int*)b;
}
int cows(long long p) {
    int cnt = 1;
    long long last = loca[0];
    for (int i = 1; i < N; ++i) {
        if (loca[i] - last >= p) {
            ++cnt;
            last = loca[i];
        }
    }
    return cnt;
}
int main()
{
    freopen("E:\\IDMdowanload\\in.txt", "r", stdin);
    long long int maxdist = 0;
    scanf("%d %d", &N, &C);
    for (int i = 0; i < N; ++i) {
        scanf("%lld", &loca[i]);
        if (loca[i] > maxdist)maxdist = loca[i];
    }
    qsort(loca, N, sizeof(loca[0]), compare);
    long long int l = 0, r = maxdist;
    while (l < r) {
        long long int mid = (l + r) / 2;
        int p = cows(mid);
        if (p < C)r = mid;
        else l = mid + 1;
    }
    
    printf("%lld", l - 1);

    return 0;
}