https://qqwhale.com/problem/5315

#include <bits/stdc++.h>
#include <iostream>
using namespace std;
int a[20][20];
int main(){
	int n,m;
	cin>>n>>m;
    for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
           // cout<<i<<" "<<j<<endl;
			cin>>a[i][j];
		}
	}
	for(int i=1;i<=n;i++){
		int x=i;
		for(int j=1,x;x>=1;x--,j++){
			cout<<a[j][x];
		}
	}
	return 0;
}

RE?????????