#include <stdio.h>

int main() {
    int n = 0;
    int m = 0;
    scanf("%d %d", &n, &m);
    int sum = 0;
    int a = 0;
    for(int i = 0; i < n; i++){
        for(int j = 0; j < m; j++){
            scanf("%d", &a);
            if(a >= 0)
                sum = sum + a;
        }
    }
    printf("%d", sum);
    return 0;
}