为什么无法输入？求解！！！

#include<bits/stdc++.h>
using namespace std;
/*int read()
{
    int r=0,f=1;char c=getchar();
    while((c<'0'||c>'9')&&c!='-')c=getchar();
    if(c=='-')
    {
        f=-1;
        c=getchar();
    }
    while(c>='0'&&c<='9')
    {
        r=r*10+c-'0';
        c=getchar();
    }
    return r*f;
}*/
int main()
{
    int n,m,s[1001][1001];
    int i,j,x1,x2,y1,y2;
    cin>>n>>m;
    for(i=1;i<=m;i++)
    {
        cin>>x1>>y1>>x2>>y2;
        s[x1][y1]+=1;
        s[x2+1][y1]-=1;
        s[x1][y2+1]-=1;
        s[x2+1][y2+1]+=1;
    }
    for(i=1;i<=n;i++)
    {
        for(j=1;j<=n;j++)
        {
            s[i][j]=s[i-1][j]+s[i][j-1]-s[i-1][j-1];
            cout<<s[i][j]<<" ";
        }
        cout<<endl;
    }
    return 0;
}