#include<stdio.h>

int main()
{
    fopen("filip.in","r");
    fopen("filip.out","w");
    int a[100][100];
    int i,j,m,n,s;

    scanf("%d%d",&n,&m);

    for(i=0;i<n;i++)
        for(j=0;j<m;j++)
            scanf("%d",&a[i][j]);
       s = 0;
     for(i=0;i<n;i++)
        for(j=0;j<m;j++)
        if(a[i][j]>=0){
        s=s+a[i][j];
        }

    printf("%d",s);

    return 0;
}