不能白嫖（疯狂暗示）

#include<bits/stdc++.h>
using namespace std;
string add(string s1,string s2)
{
    int a[10005] = {0},b[10005] = {0},c[10005] = {0};
    int len1 = s1.size(),len2 = s2.size();
    for(int i=0;i<len1;i++)
        a[i] = s1[len1-i-1]-'0';
    for(int i=0;i<len2;i++)
        b[i] = s2[len2-i-1]-'0';
    int len = max(len1,len2);
    for(int i=0;i<len;i++){
        c[i]+=a[i]+b[i];
        c[i+1]+=c[i]/10;
        c[i]=c[i]%10;
    }
    if(c[len]) 
        len++;
    string ans="";
    for(int i=len-1;i>=0;i--)
        ans+=c[i]+'0';
    return ans;
}
int n;
string f[5005];
int main(){
    f[1]="1";
    f[2]="2";
    cin>>n;
    for(int i=3;i<=n;i++)
        f[i]=add(f[i-1],f[i-2]);
    cout<<f[n];
    return 0;
}