Help！

#include <iostream>
#include <cstdio>
using namespace std;
int n,m,i,j,sum,ans,a[1010][1010];
char c;
int main(){
	scanf("%d%d",&n,&m);
	for(i=1;i<=n;i++){
		getchar();
		for(j=1;j<=m;j++){
			scanf("%c",&c);
			a[i][j]=c-'0';
			if(a[i][j]>0) ans++;
		}
	}
	for(i=1;i<=m;i++){
		sum=0;
		for(j=1;j<=n;j++)
			if(a[j][i]>a[j-1][i])
				sum+=a[j][i]-a[j-1][i];
		ans+=sum;
	}
	for(i=1;i<=n;i++){
		sum=0;
		for(j=1;j<=m;j++)
			if(a[i][j]>a[i][j-1])
				sum+=a[i][j]-a[i][j-1];
		ans+=sum;
	}
	printf("%d\n",ans*2);
	return 0;
}