CF 189A Cut Ribbon

#include<bits/stdc++.h>using namespace std;const int maxn = 4000 + 131;int n, a, b, c;int Dp[maxn];int main(){    ios::sync_with_stdio(false);    cin.tie(0);    cin >> n >> a >> b >> c;    memset(Dp,0,sizeof(Dp));    Dp[a] = Dp[b] = Dp[c] = 1;    for(int i = 0; i <= n; ++i)    {        /// 前一种状态必须是被填过的        if(i >= a && Dp[i-a]) Dp[i] = max(Dp[i], Dp[i-a]+1);        if(i >= b && Dp[i-b]) Dp[i] = max(Dp[i], Dp[i-b]+1);        if(i >= c && Dp[i-c]) Dp[i] = max(Dp[i], Dp[i-c]+1);    }    cout << Dp[n] << endl;}